Human sources of radiation released into the atmosphere over the past 60 years, although serious, pale in comparison to the radionuclides already naturally present in the ocean. (Illustration by Jack Cook, courtesy Coastal Ocean Institute, Woods Hole Oceanographic Institution)

Since the Chernobyl accident in June of 1986, the "Cafe Thorium" lab has been actively pursuing studies of the Black Sea using fallout from the event and from weapons testing, as well as naturally occurring radionuclides as tracers of oceanographic processes.

FAQ: Radiation from Fukushima

On March 11, 2011, a magnitude 9.0 earthquake—one of the largest ever recorded—occurred 80 miles off the coast of Japan. The earthquake created a series of tsunamis, the largest estimated to be over 30 feet, that swept ashore. In addition to the tragic human toll of dead, injured, and displaced, the earthquake and tsunamis badly damaged the Fukushima Daiichi nuclear power plant, eventually causing four of the six reactors there to release radiation into the atmosphere and ocean.

Since mid-2011, I have worked with Japanese colleagues and scientists around the world to understand the scope and impact of events that continue to unfold today. In June 2011, I organized the first comprehensive, international expedition to study the spread of radionuclides from Fukushima into the Pacific, and I or members of my lab have participated in several other cruises and analyzed dozens of samples of water, sediment, and biota. In addition, I began my career in oceanography by studying the spread of radionuclides from Chernobyl in the Black Sea. These are a few of the most common questions that people have been asking me lately.-Ken Buesseler, Woods Hole Oceanographic Institution

What has been released from the Fukushima reactors and how dangerous is it?

So far, we know that releases from the Fukushima reactors have been primarily composed of two radioactive substances: iodine-131 and cesium-137. In large doses, both of these isotopes or radionuclides, as they are called, can cause long-term health problems. So far, however, only those working at the plant face the most serious exposure.

Are the continued sources of radiation from the nuclear power plants of concern?

The site of the Fukushima Dai-ichi nuclear power plant is an ongoing source of radionuclides (pdf) in to the ocean—something I've seen evidence of in my data and published about since 2011. Although the numbers sound large (300,000 gallons of water leaked or 20 trillion bequerels per liter), we calculated in 2011 when radiation levels were much higher than today that the dose to someone on a ship or in the ocean was not of concern. For the workers at the site, direct exposure from leaking storage tanks is of greater health concern because exposure from these concentrated sources is much higher. For the general public, it is not our direct exposure, but uptake by the food web and, hence, the potential for human consumption of contaminated fish that is the main health concern.

Will radiation be of concern along U.S. and Canadian coasts?

Levels of any Fukushima contaminants in the ocean will be many thousands of times lower after they mix across the Pacific and arrive on the West Coast of North America in 2014. This is not to say that we should not be concerned about additional sources of radioactivity in the ocean above the natural sources, but at the levels expected even short distances from Japan, the Pacific will be safe for boating, swimming, etc.

How does CMER measure radiation in seawater samples?

We use a method that is capable of detecting extremely low levels of the specific radioactivity produced by cesium isotopes released from Fukushima in seawater. First we pass a seawater sample through a column of cesium-absorbing beads made of a resin that has been optimized for use with seawater. Then we dry the resin and place it in a high-purity germanium well detector made by Canberra Industries for between 36 and 72 hours.

Every time a cesium atom decays, that event is registered in the instrument's detector, which has the ability to discern energy given off by two critical isotopes of cesium: 134Cs and 137Cs. By counting the decay events associated with each isotope, we can calculate the total counts per second (cps) for a given sample. Knowing the efficiency of our detectors and something about the decay properties of the isotopes allows us to calculate the concentration of both cesium isotopes in a sample. This number is often reported in activity units of Bequerels per cubic meter (Bq/m3), where one Bq equals one decay event per second and one cubic meter equals 1,000 liters (about 264 gallons).

We regularly participate in proficiency tests with the International Atomic Energy Agency (IAEA) to ensure that our results are not just precise, but extremely accurate when compared to international seawater standards. In general, larger sample sizes (we process a relatively large 20 liter sample), longer counting times (we typically leave a sample on for 48 hours or more), and more efficient detectors (we use some of the world’s most sensitive gamma detectors) lead to the lowest possible detection limits.

I have a Geiger counter. Can I use it to detect radiation from Fukushima?

There are two basic types of radiation detectors—those that measure only the number of times radiation interacts with the instrument, and those that measure the energy level (in electron volts) of the particles or waves detected by the instrument. The Geiger-Mueller tube (Geiger counter) is perhaps the most widely known radiation detector and falls into the first category.

Geiger counters can measure beta particles and gamma rays (the detector window will block most alpha particles), but cannot distinguish between the two. These interactions, and the decay events that trigger them, are registered as counts or audible clicks. In general, a Geiger counter will always produce some clicks, often 20 to 40 per minute, as a result of natural sources of radioactivity around us at all times, including rocks, soil, buildings and cosmic particles. These background count rates vary widely depending upon local geology, altitude (higher at higher elevations), and even construction materials and building design (the accumulation of radon in basements is just one example). Detecting contamination from Japan above this background with a Geiger counter is impossible unless you are near the reactors and storage tanks at Fukushima, or in some of the more contaminated regions near the reactor complex, as they are not particularly sensitive instruments.

In addition, Geiger counters cannot measure the energy level of the radiation being emitted, a very important factor in determining whether the source of radiation is manmade or natural. For example, the high count rates detected by a Geiger counter along a beach near San Francisco were most likely not caused by cesium from Fukushima as originally reported, but rather caused by naturally occurring thorium-bearing minerals that are common and often elevated in some beach sands.

Are there other ways to detect Fukushima radiation in the ocean?

In addition to measuring bulk seawater samples, as we do, other labs have analyzed radiation in fish and kelp. The studies provide much-needed information that seawater samples do not, but also present some issues of their own. Analyzing fish and other seafood, for example, tells us how much radiation a person or other marine animal might be exposed to by eating the contaminated organism, but it does not tell us how far the plume has spread from Fukushima or the concentration of the various radionuclides in the water where the organism was exposed.

Studies of kelp provide integrated time averaged, qualitative measure of kelp exposure to a wide range of radionuclides in the ocean, but do not give a precise indication of the exact level of the radionuclides at a given point in time in the ocean, as levels in kelp will vary not just with water concentration changes during the kelp growth cycle, but also variables such as ocean currents, and kelp physiology.

Where does radiation from Fukushima go once it enters the ocean?

The spread of cesium once it enters the ocean can be understood by the analogy of mixing cream into coffee. At first, they are separate and distinguishable, but just as we start to stir the cream forms long, narrow filaments or streaks in the water. The streaks became longer and narrower as they moved off shore, where diffusive processes began to homogenize and dilute the radionuclides. In the ocean, diffusion is helped along by ocean eddies, squirts, and jets that broaden, mix, and continue to dilute the cesium as it travels across the ocean. With distance and time, radionuclide concentrations become much lower in the ocean, something that our measurements confirm.

How far can radiation travel?

Ionizing radiation itself cannot travel very far through the air. Typically, dust and other particles, seawater and other liquids, or even gases become radioactive due to exposure to radionuclides and are then transported great distances. In the months and years after the explosion at the Chernobyl nuclear power plant in Ukraine scientists were able to track the spread of radioactive material in the atmosphere and the ocean around the globe. Within a week after the explosions at the Fukushima plant, there were reports of very small increases in the continental U.S.

Is radiation exposure from the ocean and beach a concern?

I stood on a ship two miles from the Fukushima reactors in June 2011 and as recently as May 2013, and it was safe to be there (I carry radiation detectors with me) and collect samples of all kinds (water, sediment, biota). Although radioactive isotopes in the samples and on the ship were measurable back in our lab, it was low enough to be safe to handle samples without any precautions. In fact, our biggest problem is filtering out natural radionuclides in our samples so we can measure the trace levels of cesium and other radionuclides that we know came from Fukushima.

How long is the radiation from Fukushima a risk to humans and the environment?

Radioactive materials are, by their very nature, unstable and decline in concentration over time. This change is measured in half-lives—the length of time it takes for the radiation to decrease by one-half. Every radioactive substance has a different half-life, ranging from fractions of a second to billions of years. Those with longer half-lives are potentially more difficult to deal with because they remain radioactive for longer periods of time. Cesium-137, for example, has a half-life of 30 years and so is a potentially serious health threat for decades or centuries. Iodine-131, on the other hand, has a half-life of just 8 days and so loses much of its potency after just days and effectively disappears after one to two months.

Are there different types of radiation?

In general, there are two types of radiation, ionizing and non-ionizing. Non-ionizing radiation includes visible light and radio waves—things that, as the name implies, do not have the ability to form charged ions in other materials. Ionizing radiation, however, can and as a result presents a serious health threat because it can alter the atomic structure of living tissue. Ionizing radiation also comes in several different types, including alpha, beta, and gamma radiation, all with different degrees of concern and health impacts.

What is the normal background level of radiation?

The normal background level of radiation is different for different places on the planet. Radiation in some places is higher because these receive less of the natural protection offered by Earth’s atmosphere or because they are in places where the surrounding rocks contain more radioactive substances, such as radon. In the ocean, the largest source of radiation comes from naturally occurring substances such as potassium-40 and uranium-238, which are found at levels 1,000 to 10,000 times higher than any human sources of radiation (see illustration). The largest human release of radionuclides was the result of atmospheric nuclear weapons tests carried out by the U.S., French and British during the 1950s and 60s. Despite even the high concentration of nuclear fallout in the Pacific caused by U.S. tests on the Marshall Islands, there is no known adverse health effect associated with eating seafood from the Pacific.

How will the radioactive material released in Japan affect humans?

Unless we learn that the type or amount of material released is larger than reported or changes dramatically it will likely have significant long-term impacts only within a few miles or tens of miles from the plant. This is because the further the radioactive material travels, the more dispersed (and the less harmful) it becomes. The effects of Chernobyl were felt well beyond Ukraine in part because the amount of radioactive material released was large and because it also included substances such as plutonium that have very long half-lives. That being said, people who live near the plants would be wise to follow the minimum safe distance restrictions and other precautions recommended by the Japanese government and at-risk individuals should take suggested extra precautions such as taking potassium iodide to avoid thyroid problems.

What is the state of fisheries off Japan and along U.S. West Coast?

The coastal fisheries remain closed in Japan near Fukushima, where there is a concern for some species, especially the bottom dwelling ones, which are being tested and many have been found to be above the Japanese government's strict limits for cesium in seafood. These contaminated fish are not being sold internally in Japan or exported. Because of the dilution that occurs even a short distance from Fukushima, we do not have a concern about the levels of cesium and other radionuclides in fish off the West Coast of the U.S.

Are fish such as tuna that might have been exposed to radiation from Fukushima safe to eat?

Seawater everywhere contains many naturally occurring radionuclides, the most common being polonium-210. As a result, fish caught in the Pacific and elsewhere already have measurable quantities of these substances. Most fish do not migrate far from home, which is why fisheries off Fukushima remain closed. But some species, such as the Pacific bluefin tuna, can swim long distances and could pick up cesium in their feeding grounds off Japan. However, cesium is a salt taken up by the flesh that will begin to flush out of an exposed fish soon after they enter waters less affected by Fukushima. By the time tuna are caught in the eastern Pacific, cesium levels in their flesh are 10-20 times lower than when they were off Fukushima. Moreover, the dose from Fukushima cesium is considered insignificant relative to the dose from naturally occurring polonium-210, which was 1000 times higher in fish samples studied, and both of these are much lower relative to other, more common sources, such as dental x-rays.

Is there concern about other radionuclides, such as strontium-90?

The continued release of radionuclides from groundwater and leaking tanks at Fukushima nuclear power plants site needs to be watched closely, as the character or mix of radionuclides is changing. One example is the higher levels of strontium-90 contained in groundwater and storage tanks that are leaking into the ocean. Because strontium-90 mimics calcium, it is taken up by and concentrated in bones, where it remains for long periods of time (it has a half-life of 30 years and calcium/strontium is not replaced as quickly in the body as cesium). If leaks of strontium-90 continue, this radionuclide could become a larger concern in small fish such as sardines, which are often eaten whole. So far, however, evidence suggests that levels in fish of strontium-90 remains much lower than that of cesium-137.

If there are warnings in Japan about eating certain products contaminated by radiation, how can it be safe to eat any seafood from there?

Except for the vicinity of the reactors, seafood and other products taken from the Pacific should be safe for human consumption. Radiation levels in seafood should continue to be monitored, of course, but radiation in the ocean will very quickly become diluted and should not be a problem beyond the coast of Japan. The same is true of radiation carried by winds around the globe. However, crops and other vegetation near the reactor site (including grass that cows eat to produce milk) that receive fallout from the atmosphere build up radioactivity can remain contaminated even if washed. When these foods are consumed, a person receives much of this dose internally, often a more severe pathway to receive radiation than by external exposure.

Is debris washing ashore on the US/Canadian West Coast of concern?

Debris washed out to sea by the tsunami does not carry Fukushima radioactive contamination—I’ve measured several samples in my lab. It does, however, carry invasive species, which will be of serious concern to coastal ecosystems on the West Coast.

Have there been increased deaths as a result of radiation from Fukushima?

Reports of increased deaths are simply not true. Read this reasoned response in Scientific American to the most often-cited "scientific" paper about erroneously linking deaths to radiation from Fukushima. That article ends “This is not to say that the radiation from Fukushima is not dangerous (it is), nor that we shouldn’t closely monitor its potential to spread (we should).” I agree with that statement.

How does radiation released from the Japanese reactors compare to the accident at Chernobyl?

We still don’t know exactly how much radiation was released at Fukushima or how much will ultimately be released before the reactors are fully contained. The Chernobyl accident was much more violent and resulted in a complete breach of the reactor vessel. The event also started a very hot graphite fire that released large amounts of radioactive material into the atmosphere equivalent to between 3 and 5 percent of the total reactor inventory. Winds carried the radioactive fallout first to the north and eventually into the Black Sea to the south. Radiation in the Black Sea and Baltic Sea, though elevated, remained well below EPA guidelines for radiation in drinking water.

Why is this event of interest to oceanographers?

Oceanographers use substances called tracers to study the path and rate of ocean currents and of processes such as mixing that are important parts of the global ocean and climate systems. There are many different radionuclides that scientists use as "clocks" to measure how fast the ocean mixes and sediment accumulates on the seafloor. Some of these substances are natural, but many are the result of human activity, such as the Chernobyl accident or nuclear weapons testing, and now releases at Fukushima.